title: Moderating mycorrhizas: arbuscular mycorrhizas modify rhizosphere chemistry and maintain plant phosphorus status within narrow boundaries.
abstract: Pastures often experience a pulse of phosphorus (P) when fertilized. We examined the role of arbuscular mycorrhizal fungi (AMF) in the uptake of P from a pulse. Five legumes (Kennedia prostrata, Cullen australasicum, Bituminaria bituminosa, Medicago sativa and Trifolium subterraneum) were grown in a moderate P, sterilized field soil, either with (+AMF) or without (-AMF) addition of unsterilized field soil. After 9-10 weeks, half the pots received 15 mg P kg(-1) of soil. One week later, we measured: shoot and root dry weights; percentage of root length colonized by AMF; plant P, nitrogen and manganese (Mn) concentrations; and rhizosphere carboxylates, pH and plant-available P. The P pulse raised root P concentration by a similar amount in uncolonized and colonized plants, but shoot P concentration increased by 143% in uncolonized plants and 53% in colonized plants. Inoculation with AMF decreased the amount of rhizosphere carboxylates by 52%, raised rhizosphere pH by ∼0.2-0.7 pH units and lowered shoot Mn concentration by 38%. We conclude that AMF are not simply a means for plants to enhance P uptake when P is limiting, but also act to maintain shoot P within narrow boundaries and can affect nutrient uptake through their influence on rhizosphere chemistry.
authors.affiliation: School of Plant Biology and Institute of Agriculture, The University of Western Australia, 35 Stirling Highway, Perth, Western Australia, 6009, Australia; Future Farm Industries Cooperative Research Centre, The University of Western Australia, 35 Stirling Highway, Perth, Western Australia, 6009, Australia.
authors.forename: Nazanin K
authors.initials: NK
authors.lastname: Nazeri
authors.forename: Hans
authors.initials: H
authors.lastname: Lambers
authors.forename: Mark
authors.initials: M
authors.lastname: Tibbett
authors.forename: Megan H
authors.initials: MH
authors.lastname: Ryan
mesh_terms: D000704:Analysis of Variance; D002264:Carboxylic Acids / Q000378:metabolism; D015169:Colony Count, Microbial; D006863:Hydrogen-Ion Concentration; D016014:Linear Models; D008345:Manganese / Q000378:metabolism; D038821:Mycorrhizae / Q000254:growth & development / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism*; D018515:Plant Leaves / Q000033:anatomy & histology; D018520:Plant Shoots / Q000378:metabolism; D010944:Plants / Q000378:metabolism* / Q000382:microbiology*; D058441:Rhizosphere; D036226:Seedlings / Q000033:anatomy & histology; D013045:Species Specificity
chemical_list: D002264:Carboxylic Acids; D010758:Phosphorus; D008345:Manganese; D009584:Nitrogen
keywords: mycorrhiza-mediated resource partitioning; phosphorus pulse; rhizosphere carboxylates; rhizosphere pH; root exudates